James Cameron will reunite with the duo on-set later this year when production is scheduled to begin. Much like Peter Jackson's "The Hobbit," all three untitled "Avatar" sequels will film back-to-back, with the first follow-up set for a December 2016 release date. The second and third sequels will hit theaters in December 2017 and December 2018.

"Jake Sully is a rare combination of passion, strength, street smarts and soul, which requires a lot from an actor," Cameron said in a press release. "Sam brought to the role a combination of sensitivity, vulnerability and strength. Zoe captured every aspect of the character I envisioned, bringing to Neytiri a mix of delicacy, fierceness and incredible physicality. I am beyond pleased they'll be returning with us to Pandora."

Also reprising his role in the films is Stephen Lang, who played the ill-fated Miles Quaritch.

Fox recently revealed that Cameron would expand his planned two-sequel series to three, and that a group of screenwriters had already been hired to collaborate with the filmmaker on the scripts. Penning "Avatar 2," "Avatar 3" and "Avatar 4" are Josh Friedman ("War of the Worlds"), Rick Jaffa and Amanda Silver ("Rise of the Planet of the Apes"), and Shane Salerno ("Savages").

2014 is shaping up to be a big year for Saldana. Later this summer, she'll star in Marvel's "Guardians of the Galaxy" and just last week the actress was cast in NBC's miniseries reboot of "Rosemary's Baby."

"To be able sink your teeth into such meaty characters and to be part of such a story that is very unique and obviously has everything that I love," she recently told MTV News of her role in "Guardians." "It has space. It has a kooky director. It literally has cojones. It has amazing actors that you would have never thought to put them together. Somehow, we're all here giving 150 percent and loving the story that we're doing."